1. Field of the Invention
This invention relates to a method for manufacturing an attaching sleeve for a floating nut assembly. Further provided are the attaching sleeves formed by the method of the present invention.
2. Description of Related Art
Nut plates have been used extensively on panels and other parts for holding a nut to a panel so that the nut is always available with limited floating movement of the nut being permitted so that it can be more easily engaged by a bolt. Such a fastening device includes a receptacle which is provided by a flat plate from which portions are bent to engage and retain flanges projecting from the nut. This holds the nut to the receptacle while allowing movement of the nut.
Nut plates typically were installed on a panel or other workpiece by drilling accurately spaced openings for rivets through the panel. Several of these openings were used to secure the receptacle to the panel with the rivets. This is a time-consuming and relatively expensive operation.
Efforts have been made to provide a floating nut plate which avoided the use of the rivets for attachment to the panel. This was done by providing a knurled sleeve to fit in the opening in the panel. The knurled sleeve would become embedded in the panel and resist rotation. Tubular portions were provided on such sleeves having straight knurls on the periphery of the tube to dig into the wall of the opening in the panel. This operated to prevent rotation of the nut plate. However, this design had the disadvantage that the knurl didn't fit the wall of the opening tightly enough. It didn't embed itself securely in the wall of the opening, gripping with low torque resistance. When a bolt was subsequently engaged by the nut plate, the entire nut plate turned with the bolt, which prevented the bolt from being threaded into the nut, and sometimes the bolt fell out of the nut.
U.S. Pat. No. 3,695,324 is included in such floating nut assemblies, which provides a lightweight floating nut arrangement having a sleeve member with a tubular section that extends through a hole in the panel. Attachment of the assembly to the workpiece was accomplished by extending a tubular section through the single opening in the workpiece. A straight knurl was provided on the tubular portion and became embedded in the periphery of the opening in the panel which thereby prevented rotation of the assembly.
One disadvantage of that design, as well as previous designs, results from the method for manufacturing the attaching sleeve. Those methods produce sleeves with knurls that do not securely embed in the wall of the opening of the workpiece. This is due to an imprecise and inaccurate method for forming knurls on the tubular section. Knurls or ridges are typically formed by a rolling knurl tool rolled around the tubular sleeve, forming a plurality of knurls or ridges. The placement of these ridges, however, is difficult to precisely control. As a result, difficulties are encountered in placing the knurls or ridges on the tubular sections precisely in line with recesses formed in the wall of the opening of the workpiece or panel, particularly when the panel or workpiece is formed of very hard material where such mating recesses in the panel are employed. As a result, slippage may occur between the tubular section and the workpiece when a bolt is subsequently engaged by the nut assembly.
One obvious disadvantage of these nut assemblies is that they may lead to inefficiencies in bolt installation caused by nut slippage, or loosening of the entire assembly prior to bolt installation. It would be desirable to have a floating nut assembly in which this slippage between the nut assembly and the wall of the opening of the workpiece was eliminated by a method of manufacture which accurately and precisely places ridges or ribs on the tubular section that securely fit into and mate with recesses placed on the wall of the opening of the workpiece.
A further disadvantage encountered in the manufacture of prior floating nut assemblies, and in particular with attaching sleeves involved in floating nut assemblies, is the large number of steps required to manufacture these pieces. They are manufactured as piece work, requiring drilling, stamping, knurling, and other machining steps. These multiple manufacturing steps are expensive. Furthermore, the resulting parts are not identical. Large variations from piece to piece are seen in the critically fitting areas of the piece, such as the knurls or ridges. In addition, the drilling and other steps result in much unnecessary scrap metal.
It would be desirable to provide a method of manufacture which reduces the number of steps in forming such attaching sleeves. It would be further desirable for such a method to provide accurate, precise, and consistent placement of ridges or knurls. Further desired would be a manufacturing method which produces attaching sleeves which consistently fit the workpiece opening snugly with sufficient torque resistance to make bolt installation efficient in workpieces requiring floating nut assemblies. Also desirable would be a manufacturing method which operated automatically with rate of production much higher than piece-work manufacture.